


The Big Date

by TellTaleKael



Category: Undertale (Video Game)
Genre: Blue Is Excited And Slim Adores Him, Blue/Slim, Body Worship, Commission fic, Getting Naughty Under The Table, Going on a date, M/M, Praise Kink, Semi-Public Sex, Smut, Underswap Sans/Fellswap Papyrus
Language: English
Status: Completed
Published: 2021-01-11
Updated: 2021-01-11
Packaged: 2021-03-15 21:35:08
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,175
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28695534
Author URL: https://archiveofourown.org/users/TellTaleKael/pseuds/TellTaleKael
Summary: It was Blue’s turn to take Slim out, and it would be the first time Slim would stay the night in Underswap, so it had to be perfect!
Relationships: Papyrus/Sans (Undertale)
Comments: 6
Kudos: 32





	The Big Date

**Author's Note:**

> This is a commission fic for [idek_uggy](https://twitter.com/idek_uggy?s=21) on Twitter. Enjoy!

“-and if you need anything, just call me,” Stretch was saying as Blue all but shoved him out of the front door.

“Yes, Brother, I know!”

“i mean for anything. no matter what it is. if you feel unsafe-“

“I’m having a romantic evening with my datemate, not going on an epic adventure across the multiverse! Why would I feel unsafe?”

“i’m not saying you will, just that if you do-“

“And I am saying that I’m tired of your distrust of my datemate! Or did you forget he’s technically you?”

Stretch made a face of discomfort at that, sockets scrunching up. “don’t say it like that.”

“Then go have your sleepover with Undyne and let me get ready for my date,” Blue shot back. “We both know you’ve already given Slim the customary ‘big brother’ talk, and the fact that he’s still alive means that he passed your conditions. You have no reason to act like this.”

“but-“

“No! I will not listen to your buts!” Blue made a sweeping motion with his hands. “Shoo! I will see you tomorrow!” And then he closed the door, leaving Stretch out on the front steps of their house. He waited until he heard the sound of Stretch teleporting away before he relaxed. Honestly, he was just as much of an adult as his brother was! He didn’t know why Stretch still treated him like a babybones sometimes. 

Blue could remember when Stretch found out about his relationship with Slim. He had accused the latter of corrupting Blue! As if Blue hadn’t had access to the Undernet before they had come to the surface, and the Internet afterwards! It had taken sharing some personal information on what Blue had discovered for himself to get Stretch to understand that he wasn’t a baby, and he knew about sex long before Slim had arrived, thank you very much!

Stretch had done better since then, but this would be the first time Blue brought Slim home after a date, instead of going to Slim’s room in Fellswap. It was a special occasion, and Blue wanted it all to go well. He had already cleaned the house from top to bottom, until everything was spotless, so it was time to get himself clean as well. 

He stepped into the shower, letting the hot water cascade down his bare bones. If there was one thing to say about the surface, the water pressure was much better than it had been back in Snowdin! He took a moment to stand there, taking a deep breath. But only a moment! He didn’t want to waste too much time.

The soap he lathered his bones with was one Slim had gotten him, handed over with a sly smirk. Blue had to admit, it did smell slightly like Slim’s scent, like burnt sugar and caramel, without the added cigarette smoke that clung to him from his occasional smokes- a habit Blue tried to discourage, but he couldn’t really complain much since Slim never smoked around him or in the house. Any house, even his own, although that could have been because Razz would never allow it.

Either way, the soap smelled close enough that showers felt like a warm hug from his datemate... or close enough when the real thing wasn’t an option.

There was also something interesting in the way Slim’s eyelights burned when Blue smelled like him, but that might have been the whole point of the gift in the first place. 

Blue spent a little longer than necessary lingering in the shower, soul fluttering over his memories of how Slim had reacted the first time Blue had shown up after using the soap, but even then he still had plenty of time to get dressed when he finally turned the water off and got out. He patted himself dry with his fluffy towel, trying not to pay too much attention to the scar on his neck. For him, it had appeared suddenly, but from what he understood when Papy finally explained it to him, it had taken many, many resets for it to be permanently etched into his bone. He normally kept it hidden under his bandana, but... Papy wasn’t around to see it, and Slim always seemed particularly fond of stroking over the sensitive area with his phalanges and tongue alike, so Blue left the scarf carefully folded up on top of his dresser while he went to grab his date clothes from the closet. 

Though not nearly as cool as his old set, the jeans and button up shirt the human had helped him pick out from one of the human stores certainly looked dashing on him anyway. Especially if he left the top button undone, allowing his collarbones to peek out just a little. He struck a pose in front of the mirror, giving his best sultry look. 

“...mweh, it’ll do,” he said after a moment, laughing at his own antics. He gave himself another once over, making sure the hem of his shirt was even. Layering a jacket over it, he declared himself as ready as he would ever be. He slipped into his nicest boots, grabbed his wallet and keys, and headed out of the door. 

The little garden shed in the backyard didn’t look like much from the outside, but taking a small flight of stairs within led to a basement. Sitting in the middle of the room was the machine that allowed them to connect to alternate universes. Blue didn’t know exactly how it worked, but apparently neither had Stretch when he pieced it together. No one had expected it when one of Blue’s alternates walked through, entering their universe with a tired grin. That was when they met Sans. The original one, apparently. Ever since then, they had been in contact with a variety of their alternates from various universes. 

There was only one skeleton he wanted to see at that moment, though. Typing in the coordinates to the correct universe, Blue fired up the machine and stepped through the resulting tear in reality. 

Slim and Razz had their machine in the basement of the house, rather than out in a cellar. Blue took a moment to make sure his clothes were nice and neat still before climbing the stairs, ascending into the house proper. The click of heels down the hall signaled Razz’s approach before he even turned the corner, mouth curled down into a light frown. It didn’t get any deeper at the sight of Blue, but it certainly didn’t curl up into a smile either.

“Oh. It’s You.” Razz looked Blue up and down, no doubt cataloging the departure from his usual clothing. “I Thought You And The Mutt Were Going On A Date?”

“We are! I’m here to pick him up,” Blue explained eagerly. “The dating manual said picking your datemate up from their house is a good start to the date!”

Razz’s eyelights rolled a little. “If You Say So. I Doubt My Brother Is Even Awake Yet-“

Razz was cut off by the sounds of Slim’s footsteps. He turned and cocked a browbone. “Well, I’ll Be Damned. I Didn’t Realize You Were So Whipped, Mutt.”

Slim gave a lazy shrug, grinning crookedly. “you know what they say, m’lord. happy wife, happy life?”

Razz scoffed. “Whatever. Even If You Screw Up This Date, You’re Not To Come Home Until Tomorrow, Do You Hear Me? I Have Maintenance To Do.” With that, he turned on his heels, swooping down the hall and disappearing around the corner.

“Maintenance?” Blue asked quietly.

“probably going to take a candlelit bath and read trashy romance novels, but he’s never going to admit that it’s self-care.” Slim ambled over, giving Blue a bright smile. “i like the new look.”

Blue blushed and gave a little spin. “It’s my new date outfit! The human helped me pick it out,” he said excitedly. When he came to a stop facing slim again, he looked his boyfriend over. “You look wonderful too!” Slim had changed his usual attire as well, opting for fitted slacks and a turtleneck, ditching the fluffy hoodie and collar he usually wore. It was certainly a date outfit, which made Blue beam. 

Slim smirked. “if you think i look good in this, you should see me out of it,” he said with a wink. Blue flushed even brighter.

“There will be time for such shenanigans later!” he chastised. “We need to go so we’re not late! I made reservations!” He offered his hand to Slim, who took it.

“reservations?”

“Yes! You’ll have to wait and see though! Come on!”

***

Back in his world, Blue hurried Slim to the car. It wasn’t a fancy motorcycle, like in his dreams, but together he and Stretch had saved up to purchase a vehicle nonetheless. Blue had even managed to get his driver’s license on his first try, passing the tests after weeks of studying. It took Stretch longer, since he mostly teleported everywhere, but the lazybones managed to get his too, just in case.

The restaurant wasn’t too far away, but it wasn’t within walking distance. Blue found a parking spot, glancing at Slim to see his reaction. 

“I know between my tacos and Razz’s enchiladas you eat quite a lot of Mexican food, so I thought we could try something different.” He looked out of the windshield at the Italian restaurant they were parked in front of. “This place had really good reviews!”

Slim smiled, a real smile instead of his usual smirk. “sounds good to me, sweets. but before we go in...” He reached across the center console to pull Blue into a quick kiss, licking across his teeth before he pulled away, looking satisfied. “there, now i’m ready.”

Blue patted his face as he stepped out of the car, willing his blush to go down. Slim surprised him often with shows of affection, so he thought he should be used to it by then, but he wasn’t. The other managed to make him heat up with just a look or a simple action, and he knew it, too! 

Hurrying, he held the door open for Slim, always trying to be the perfect gentleman for his datemate. Stepping inside, they were faced with rich smells and the soft clinking of silverware against plates. The interior of the restaurant was donned in dark colors and cozy lighting, with soft instrumental music playing in the background. Blue practically hopped up to the host. 

“Hello! We have a reservation for Blue,” he said eagerly. He had called a week ahead to be absolutely sure they could get in, even though it was probably a little overboard to call that early.

The host checked the listing. “Of course. Right this way, sirs.” 

Blue offered Slim his arm, and even though he had to slouch a little, the taller took it. Arm in arm, they followed the host to one of the more secluded tables in the back, partially blocked from view by large planters. Blue had asked for one of their more private areas when he made the reservation, so he and Slim could talk in peace. Some humans still gave monsters strange looks when they were out and about, and Blue didn’t want to have to worry; he just wanted to focus on Slim.

They sat down and the host left with a promise that their server would be by soon. As soon as they were gone, Slim stood back up, taking his chair and circling the table so he could sit beside Blue, instead of across from him.

“i want to be next to you,” he said at Blue’s curious look.

“Oh! Of course!” Blue smiled. They were definitely to the point of more closeness in their relationship, and they could still talk sitting next to one another. Blue leaned into Slim, resting his skull against the other briefly. 

He sat back up when their waitress arrived to take their drink orders and leave them with a menu. “Oh, everything looks so good,” he mused as he looked over the menu. The reviews had given no complaints about the food, so he assumed it was all as good as it looked. “I don’t know what to get. I’m torn between the ravioli and the chicken alfredo.”

Slim was leaning with his elbow on the table, chin in his hand, watching Blue with a small smile. “let’s just get both and we can share,” he suggested. 

“That’s a good idea!” Blue put his menu down and returned Slim’s smile.

“i do have them occasionally.”

“I know that!” Blue tilted his skull closer, voice lowering. “The last time we were together, I very much enjoyed your ideas.”

Slim grinned, no doubt remembering Blue spread out underneath him, blindfolded. Blue never would have guessed just how sensitive a lack of sight would make him, but every touch had been electric. He held Slim’s gaze, color rising to his cheeks as the tension grew.

They were interrupted by the waitress returning with their drinks. Her eyes cut to Blue’s flushed face, but she took their orders without any remark, writing them down and returning to the kitchen. Blue let out a soft chuckle, relaxing again.

“Goodness, we shouldn’t let our shenanigans get out of hand,” he said, chastising both himself and Slim. Slim gave him an easy grin.

“i don’t mind getting them in hand.” Before Blue could ask what he meant, he felt slender phalanges curl around his femur through his jeans. Suddenly, Slim’s shift closer made much more sense. Hidden as they were, he could get away with such bold touches. Blue inhaled deeply.

“Th-That was a terrible pun,” he accused. Slim’s hand trailed upwards slowly.

“maybe so, but it still worked.” Slim leaned down to nuzzle against Blue’s skull, looking all for the world as if he were just cuddling. But Blue was the one who felt Slim’s sneaky hand slip into his jeans. Bone rasped against bone lightly, teasingly.

“We shouldn’t do that here!” Blue protested quietly. Slim hummed against his skull. 

“you remember your safeword?”

“Yes, but-“ 

Slim swooped down, ducking halfway below the table. The long tablecloth blocked his hands from being visible as he unzipped Blue’s jeans enough to twist his wrist. He stroked Blue’s coccyx lightly, and then a little more firmly. Blue had to bite down on a gasp, fighting the urge to arch. Oh, that was too lewd for a public area! One of Slim’s phalanges teased a hole of his sacrum, making his magic collect heavily in his pelvis, unformed and swirling dangerously, throbbing slightly. Just a few more moments, and he knew his body would form without his command...

A steaming plate was placed down in front of Blue and he jumped. The waitress looked at him, at his flushed face, cocking a brow. “Is everything alright, sirs?”

Slim popped up from under the table, fork in hand. “clumsy me, i dropped this. could i please get another?” Blue didn’t even know where he had gotten the fork, or how. The waitress looked at it, before pasting on a smile.

“Of course.” She handed Slim a fresh set of silverware from her apron, taking the dirty fork from him. “Enjoy your meal, and I’ll be back to check on you in a bit.”

As soon as she was gone, Blue devolved into high pitched giggles. Slim joined him, chuckling as he carefully zipped Blue’s jeans back up.

“W-we should probably not do that again,” Blue huffed, face still stained the color of his namesake. 

“probably not,” Slim agreed, looking not the least bit sorry for his actions. He unwrapped his new silverware, plucking the fork up and twirling it between his phalanges. “at least, not until we get home,” he added with a wink. 

Blue squirmed in his seat, willing his magic to be patient. It was difficult with Slim right next to him, but the promise of food was enough of a distraction for the time being. He speared a ravioli on his fork and brought it to his mouth. Stars burst in his sockets and he hummed. “Mm, this is good!” Scooping another ravioli onto his fork, he held it up to Slim. “Try some!”

Slim accepted the bite, nodding as he chewed. “pretty good. here, try this too.” He twirled some of his noodles onto his fork and offered it to Blue. 

They continued to feed one another, Blue laughing and humming after every bite and Slim watching him with a fond expression. Everything was delicious. The reviews definitely hadn’t lied. By the time their plates were clean, Blue was afraid he was going to burst, but it had been too good to leave behind. He leaned against Slim, closing his sockets. “That was soooo good.”

Slim nuzzled against him, cooing a little. When the waitress returned to ask if they wanted dessert, Slim shook his head. “no thanks, we have dessert at home.” Blue looked at him curiously, but Slim didn’t elaborate. The check was passed over, and Blue jumped to grab it, since he was the one taking Slim out this time. His job as a security guard at the local mall didn’t pay an exorbitant amount, but it was enough. He paid as Slim stepped outside to smoke with an apologetic look, but Blue waved him off. He knew that quitting didn’t happen overnight, and Slim had been cutting back. 

Blue thanked the host after getting his receipt and stepped back outside, joining Slim by the car. “I’m curious about this dessert you’re talking about,” he admitted as he opened the car door for Slim. Slim just slid into his seat with a smirk.

***

It turned out that Blue himself was the dessert. As soon as they entered the house, Slim crowded him up against the door, pulling him into a feverish kiss. His hands slipped under Blue’s shirt to stroke at his spine, making Blue shiver against him. “i’ve been thinking about this all day,” Slim growled into the kiss. He curled his phalanges around Blue’s spine and tugged lightly. “i want to taste you. let me?”

Blue gasped and nodded, back arching as Slim tugged again. “Yes, please!” He scrambled to shuck his coat off and unbutton his shirt while Slim knelt and practically tore his jeans from his legs. His boots were tossed somewhere behind Slim, to be cleaned up later. Slim pressed his face in Blue’s pelvic inlet, running his tongue along bone before sitting back. Blue’s magic snapped into place painfully fast, from his collarbones to his knees. Slim kneaded his thighs, licking his teeth in anticipation. 

“looks good, sweets. thank you for dessert.”

Hiking one of Blue’s legs over his shoulder, Slim dove in, running his tongue across the lips of his pussy. He parted them with one hand, licking between, teasing against Blue’s entrance. He was already wet, and probably would have been since the incident at the restaurant if he had been formed. Slim purred at the discovery, pressing a kiss to Blue’s sensitive flesh. “so cute,” he murmured, teasing the tip of his tongue against Blue’s hole. “and you smell like me. you used the soap,” he purred. He continued to tease, flicking Blue’s clit with his thumb as well, until Blue was a shaking mess. Only then did he point his tongue, allowing it to slip inside, caressing and stretching Blue’s inner walls. 

Blue gasped, head thumping back against the door, phalanges scrabbling against Slim’s skull. No one he had ever been with had ever eaten him out with half as much gusto as Slim did. Sometimes, he brought Blue to the brink over and over, for as long as an hour, just with his tongue. If Blue had to guess, he would say that oral was probably Slim’s favorite act to perform. 

Blue’s phalanges were sore from clenching by the time he reached his peak. He curled over Slim, grasping his skull and rocking against him with stars in his sockets. Slim pried his hands away when Blue finally slumped against him, looking up, face stained blue with his slick. He licked his teeth clean, purring, and surged up, lifting Blue into his arms and nuzzling him. “that was good dessert,” he cooed, pushing away from the door and heading for the stairs. “i’ve still got room left, though.”

He nudged the door to Blue’s room open with his foot. It was as pristine as he had left it, with clean sheets in preparation for Slim’s first time staying over. Blue grasped Slim’s face and kissed him, tasting himself on that wicked tongue. “Then perhaps you should eat some more,” he suggested. Slim tossed him onto the bed, laughing as he bounced a little.

“oh, i plan too.”

Slim stripped with efficiency, leaving his clothes scattered all over the floor. Blue didn’t have it in him to care about the mess, especially when Slim formed his body. His cock was swollen and flushed, drooling at the tip and ready to go. 

Blue expected him to jump right in, but Slim climbed onto the bed above him and leaned down to kiss him sweetly. The frantic pace eased down to something more leisurely, and Slim leaned back to look at him with heated eyelights. “you are so cute,” he praised, dropping down to kiss Blue’s collarbone. His hand cupped one of Blue’s breasts, kneading slightly and making him moan. “so sweet for me.” Slim slipped lower, kissing Blue’s plush stomach. “soft yet so strong.” His hands slid down to squeeze Blue’s chubby thighs again. “absolutely perfect.”

Blue inhaled, toes curling as heat coursed through him. Usually, their times together were frantic and desperate, all heat and pleasure, but every once in a while, Slim would take his time like this, kissing and caressing and praising Blue all over. It never failed to make him squirm pleasantly, eyelights shifting to hazy hearts. He reached out, pulling Slim back up for another kiss. “I love you,” he said with a smile. Slim returned the smile, bracing himself on one arm, using the other to reach down and line himself up with Blue’s entrance. Blue parted his thighs, giving Slim room to settle between them. He slid inside in one long thrust, stopping when he was hilted to allow Blue to adjust to the stretch. 

“you spoil me,” Slim accused, nuzzling his face against Blue’s neck. He swiped his tongue over the scar that stretched across Blue’s neck. “i love you too.”

They stayed like that for a moment, nuzzling against one another. When Blue’s muscles finally relaxed, Slim lifted himself up on his knees, gripping Blue’s hips. The first thrust was slow, but it didn’t take long for Slim to set a quick pace. With one orgasm done, Blue was wet enough that the glide was smooth, the symphony of their ecto meeting accompanied by slick sounds. Blue panted, reaching up to curl his phalanges in Slim’s ribs. He traced his thumbs over the scars that he knew were the most sensitive. He knew Slim’s universe was rougher than his own, and where some might despise and fear the scars, he viewed them as times when he might have lost the chance to meet Slim, but didn’t. Slim had survived everything, and was there with Blue now, over him, in him. Blue was proud of Slim, and he hoped the other knew that. 

Pleasurable pressure began to build low in Blue’s gut, and he could tell by the way Slim’s thrusts grew erratic that the other was close as well. He reached his peak first, clamping down on Slim and arching off the bed, coming with a cry. Slim rocked into him, extending the sparks of white hot pleasure that raced up his spine. When Blue finally relaxed, Slim picked up the pace again, chasing his own pleasure. Blue hefted himself up with tired arms, closing his teeth around Slim’s collarbone and biting down. It was enough to push him over the edge, hilting into Blue as deep as he could and spilling hot magic inside of him. Blue moaned at the warmth that bloomed inside of him, sockets slipping shut as he let go of Slim’s collarbone. The bite would probably bruise, a fact that Slim would probably be proud of. He liked it when Blue marked him.

Blue pried his sockets open when Slim pulled out and flopped over beside him, looking just as pleased as could be. He curled around Blue, tugging him close and snuggling down into the mattress. 

“Hmm... our clothes,” Blue protested.

“they’ll still be there after a nap.” Slim kissed his temple.

“I suppose so,” Blue agreed. He knew that he would probably wake up to Slim’s hands on him again, and they would find pleasure once more, and that sounded much better than cleaning. So he curled up and closed his sockets. He could spare a short while for a nap, as long as Stretch never found out.

**Author's Note:**

> Fun fact: my phone kept autocorrecting Slim’s name to Slime and I don’t know why lol.


End file.
